She served as a Police Activities League Cadet and Civil Service Police Cadet prior to entering the department. She was sworn in as a police officer in 1977, and worked through the ranks of inspector, sergeant, lieutenant, captain, commander, deputy chief, assistant chief, acting chief, and then permanent chief. During her career, she has been assigned to patrol, served as an Academy training officer and instructor, child abuse investigator, youth programs coordinator, drug education instructor, grant writer, strategic planner, district station watch commander and commanding officer. Chief Fong was assigned to the Special Operations Division in August 1998 when she was promoted to commander. While there, she was responsible for the Traffic, Tactical, and MUNI Transit companies. In June 2000, upon promotion to deputy chief, she was assigned to the Field Operations Bureau, where she managed the uniformed patrol personnel of the San Francisco Police Department. In August 2002, she was assigned to oversee the Administration Bureau. In May 2003, she was appointed assistant chief of police. Mayor Gavin Newsom appointed her acting chief of police on January 22, 2004, and chief of police on April 14, 2004.
Firearm certification
Chief Fong drew criticism in June 2008 for failing to complete firearm recertification for over five years though all San Francisco police officers are required to recertify annually by department regulations. Chief Fong was quoted as saying that she was too busy to recertify. When the controversy erupted in the local media, she was recertified a week later.
Leadership
Fong was criticized for supporting Mayor Gavin Newsom in his conflict with police officer Andrew Cohen and 21 other officers who made a controversial "comedy" videotape for a police Christmas party. This tape was deemed racist, sexist, homophobic, and anti-Asian by the mayor, but the officers pointed out that they were making fun of themselves and that the tape was meant only for their own private Christmas party. Fong was criticized for supporting the mayor in this dispute rather than the men and women under her command.
Retirement
Fong announced in December 2008 that she would be stepping down in April 2009, after serving five years as San Francisco's police chief. Fong receives some $264,000 annually in pension payments. The high amount of pension payments to Fong and other retired top officials in San Francisco's police and fire departments has prompted critical comment.